Continuous exposure to sunlight often causes photodegradation of the dye and slight to severe color changes in dyed synthetic fabrics, such as polyester or nylon. The photodegradation process is largely caused by ultraviolet (UV) radiation. The presence of heat and moisture accelerates the rate of photodecomposition.
It is a common practice in the textile dyeing art to use colorless UV absorbers in the dyeing process to improve the light stability of the resulting dyed textiles and protect the dyed textiles from photodegradation. The UV absorbers include benzophenones and benzotriazoles, which are organic molecules capable of absorbing UV light in the range of 290-400 nanometers, and which convert the absorbed incident radiation into harmless heat. Such UV absorbers improve the UV stability of the colored polyester textiles, but only to a limited extent. The improvement in UV stability is limited to 0.5-1 grade (Gray Scale) over 200 hours of UV exposure, and this occurs only when the maximum amount, typically 3 to 5% on the weight of the fabric (OWF), of the UV absorber is used. Little or no improvement is seen at lower UV light exposures, for instance in the range of 40-100 hours even using significant amounts of UV absorbers.
An object of this invention is to develop dyed polyester fabrics exhibiting improved resistance to fading by ultraviolet light. Desirably, a significant improvement of from one to two grades (Gray Scale), comparable with the most protected commerically-available UV-stabilized fabrics is achieved.
Fabric products provided by this invention and exhibiting maximum lightfastness are typically used for drapery or curtain materials, and as automotive textiles for seats and trim use.